Lattice girder

ABSTRACT

A lattice girder comprising an upper boom, a lower boom and a plurality of braces interconnecting the booms, is produced from a grid of structural steel rods so that the braces extend in parallel planes oblique to perpendicular planes passing through the booms, the rods being spot welded at their points of intersection. The longitudinally and transversely extending rods of the grid are fed to a spot welding station in adjacent parallel planes so that the transversely extending rods extend obliquely to the longitudinally extending rods. The grid is then cut into longitudinally extending sections each forming a girder blank, and each section is bent about a longitudinally extending axis to produce the lattice girder, one of the longitudinally extending girders forming the upper boom and the transversely extending rods forming the braces.

United States Patent Grebner et al.

[ Dec. 11, 1973 LATTICE GIRDER 3,345,793 10/1967 Cvikl 52/693 x 905,056 11/1908 Coignet.... 52/693 X [76] 5;"? 'ii i g m i z 2,199,152 4/1940 Edge etal. 29/155 R g i gg f Obert 3,475,876 11 1969 Oroschakoff 52/694 x oc s r. er ar pin er, Brunhildenstr. 14, both of wiesbaden; Walter Ehemann, Primary Exammer-Pnce C. Faw, Jr. Waldstr. 127, Nauheim, all or Attorney-Kurt Kelman Germany [22] Filed: Mar. 8, 1972 [57] ABSTRACT [21] Appl 232,981 A lattice girder comprising an upper boom, a lower Related ,s Application Data boom and a plurality of braces interconnecting the [62] Division of Ser No 69 087 Sept 2 1970 booms, is produced from a grid of structural steel rods abandoned so that the braces extend in parallel planes oblique to perpendicular planes passing through the booms, the [30] Foreign Application priority Data rods being spot welded at their points of intersection. Se t 3 1969 German P 19 44 626 5 The longitudinally and transversely extending rods of i' 1970 Germany P 20 10 666's the grid are fed to a spot welding station in adjacent y parallel planes so that the transversely extending rods extend obliquely to the longitudinally extending rods. CCll. 52/693,509: The g is then cut into longitudinally extending [58] Fieid 694 690 tions each forming a girder blank, and each section is 1 29/i55 bent about a longitudinally extending axis to produce the lattice girder, one of the longitudinally extending [56] References Cited girders forming the upper boom and the transversely UNITED STATES PATENTS extending rods forming the braces. 3,036,676 5/1962 Potzsch 52/693 X 4 Claims, 11 Drawing Figures v fi, 4 1

PATENTEDBEI: H I975 3.771433 SHEET 2 OF 4 INVENTORS FR/TL GREBNEK WILHELM KoLscl-l BY Hflkp SPINDLEIQ WALTER ENE/wan AGENT LATTICE GIRDER This is a division of application Ser. No. 69,087, filed Sept. 2, 1970, now abandoned.

Lattice girders comprising a lower boom, an upper boom and diagonally extending braces connecting the booms, as well as girder blanks therefor and methods of their manufacture are known. Many difficulties have been encountered in spot welding the braces to the booms and/or in bending the structural steel rods, which form the booms and the braces, to form the three-dimensional girders from the plane blanks.

It is the primary object of this invention to overcome these manufacturing difficulties and, more particularly, to provide a blank which may be bent 180 in producing a girder whose two lower boom rods lie side-by-side and may be welded together into a unitary lower boom structure.

This and other objects are accomplished according to the invention by preparing a mat or grid of transversely spaced, longitudinally extending steel rods and longitudinally spaced, transversely extending steel rods intersecting the longitudinally extending steel rods. The longitudinally and transversely extending steel rods are fed to a spotwelding station in respective and adjacent parallel planes, and respective ones of the longitudinally extending rods are spot welded at this station to respective ones of the transversely extending rods at the points of intersection of the respective rods. The transversely extending rods extend obliquely to the longitudinally extending rods.

The transversely extending rods of the mat or grid are then cut along longitudinally extending lines to produce longitudinally extending mat or grid sections including at least two of the longitudinally extending rods. Each section is then bent about a longitudinally extending axis to produce a respective lattice girder. The bending axis may be constituted by one of the longitudinally extending rods of the section or it may be in the region of such a rod.

The resultant lattice girder comprises an upper boom, a lower boom, and a plurality of braces interconnecting the booms, the braces extending in parallel planes which are oblique to perpendicular planes passing through the booms.

The plane mat or grid of structural steel rods, which serves as a blank forproducing the lattice girders, comprises transversely spaced, longitudinally extending steel rods in one plane, wherein groups of at least two such rods form longitudinally extending sections, and the transverse spacing of adjacent rods of adjacent sections is smaller than the transverse spacing of adjacent rods of each section. Longitudinally and equidistantly spaced, transversely extending steel rods extend obliquely to the longitudinally extending rods in a plane adjacent and parallel to the one plane. At their points of intersection, the rods are spot welded to each other.

Such plane mats may be prepared in simple spot welding machines to which the structural steel rods are fed in straight path and without prior bending of the transverse rods designed to form the braces of the lattice girder. Also, these transverse rods may be bent easily through 180 so that the conventional rod gages may be used in the manufacture of the girders.

Furthermore, any desired portion of the blank sections may be readily adapted to support heavier loads simply by feeding additional and more closely spaced transverse rods to the spot welding machine so as to produce stronger bracing portions at given locations of the girders.

Conventional lattice girders of the general type hereinabove described comprise one upper boom structural steel rod, two lower boom structural steel rods, and diagonalbraces interconnecting the booms, each brace consisting of a generally V-shaped structural steel rod. in the girder of the present invention, the braces extend in planes which are oblique to the perpendicular planes passing through booms, which means that the rods of the braces must be bent into their V-shape in a transverse plane which is oblique to the axis of the brace rod. This makes the bending rather difficult and requires bending moments of considerable force produced by special machinery. When the longitudinal section of the blank is bent about the longitudinally extending axis, for instance the upper boom rod, the second lower boom rod in the girder half which is being bent about this axis is supposed to force all the brace ends attached to this second lower boom rod to pass through the same bending path. However, for static reasons, the gage of the brace rods is larger than that of the lower boom rods. Therefore, the opposite effect has been observed, i.e., the braces deform the lower boom rod into an undulant shape.

According to this invention, this difficulty has been avoided by providing only a single lower boom rod. The ends of the braces have stubs extending beyond the lower boom, and these stubs have portions extending in the direction of the boom. A first leg of the braces is connected to the single lower boom rod while the second leg extends freely into the plane of the lower boom. Both legs have the stub portions which support the transverse structural steel rods of a reinforcing mat or grid extending parallel to, and below, the lower boom.

In this embodiment, the second brace leg of bentover half of the girder moves freely, rather than being restrained by a lower boom rod attached thereto, which makes the bending much easier. Moreover, the bentover part of the girder has no spot welds which may be deformed and damaged by bending.

All that needs to be done to produce such a girder is to eliminate one of the longitudinally extending rods from the longitudinal sections of the mat or grid, which forms the girder blank. In the completed girder, the missing lower boom rod is statically replaced by the reinforcing mat. No other changes are required in mass producing the blank.

The ends of the braces may carry detachable or fixed spacing elements, for instance of synthetic resin, to define the necessary thickness of the concrete slab attached to the girder. These spacing elements may consist simply of perpendicularly projecting ends of the braces, which may be coated with synthetic resin or carry synthetic resin sleeves, so that the girders may rest on the bottom of the concrete form on these spacing elements. The synthetic resin will protect the spacing elements against corrosion.

The above and other objects, advantages and features of the present invention will become more apparent from the following detailed description of certain now preferred embodiments thereof, taken in conjunction with the accompanying drawing wherein FIG. 1 is a top view of a structural steel mat or grid useful in the production of lattice girders according to this invention;

FIG. 2 is a perspective view of a lattice girder consisting of a cut-out and expanded section of the mat or grid of FIG. 1;

FIG. 3 is a side view of the lattice girder of FIG. 2;

FIG. 4 is a transverse section of the lattice girder of FIG. 2;

FIG. 5 is a transverse section of the lattice girder after it has been pressed together'in a transverse direction;

FIG. 5a shows-a modified mat or grid for forming the girder of FIG. 5;

FIG. 6 is a side view of a modified lattice girder connected to a reinforcing mat or grid;

FIG. 7 is a schematic top view showing the feeding of the longitudinally and transversely extending structural steel rods of the mat or grid of FIG. 1 to a spot welding machine;

FIG. 8 is a side view of another embodiment of a lattice girder;

FIG. 9 is a transverse section along line IIX of FIG. 8; and

FIG. 10 is a perspective view of the girder of FIGS. 8 and 9, connected to a reinforcing mat or grid.

Referring now to the drawing, wherein like reference numerals indicate like parts functioning in a like manner in all figures to avoid redundancy in the description, FIG. 1 shows transversely spaced, longitudinally extending structural steel rods 1. The rods are formed into groups of three equidistantly spaced, parallel rods forming sections of the mat or grid, a smaller transverse spacing being provided between the longitudinally extending rods 1', 1' of adjacent sections. After the structural steel mat or grid has been welded together, the sections are cut apart along cut lines 3 or 3' or 3" between the closely spaced rods 1', 1', as will be explained more fully hereinafter.

Longitudinally spaced, transversely extending structural steel rods 2 intersect the rods 1, the rods 2 lying in a plane immediately adjacent the plane of the rods 1 so that the rods contact each other at their points of intersection where they are spot welded to each other. The rods 2, which are parallel to each other, extend obliquely to rods 1 at any desired angle other than perpendicular.

As indicated in broken lines, at locations requiring particular strength, additional transverse rods 2' may be provided at desired distances between pairs of regular rods 2.

The feeding of the rods 1 and 2 to a spot welding machine 7 is schematically shown in FIG. 7. At the welding station, the rods are spot-welded together to form the mat or grid of FIG. 1, whereupon it is cut into sections which provide blanks for the lattice girders. If the cut lines are centrally intermediate the longitudinally extending rods 1, 1' of adjacent sections, as shown at 3, the transversely extending braces of the resultant lattice girders will have stubs 4 laterally extending beyond the lower boom rods 1, 1' (see FIG. 4). If the cut lines extend close to the respective rods 1', 1', as shown at 3', the braces will end close to the lower booms. If the cut lines extend close to rods 1', 1' at alternating rods 2, as shown at 3", only alternating braces will have stubs 4.

After the mat or grid has been cut into sections, each section is bent about a longitudinally extending axis formed by rod 1 or in the range of rod 1 to produce the lattice girder shown in FIGS. 2 and 3. Such a girder is of triangular cross section and has a lower boom including a pair of lower boom rods 1, 1', an upper boom 1 and diagonally extending braces 2 connecting the upper boom to the lower boom. Each brace extends in a plane which is oblique and transverse to the perpendicular planes passing through the booms of the girder, the braces extending from the outside of the lower rods over the upper boom.

In the embodiment of FIG. 5, the braces 2 of the lattice girder have been pressed together so that the lower boom rods 1', 1 contact each other. If desired, the contacting lower boom rods may be spot-welded together so as to constitute a unitary lower girder boom. For the production of this type of lattice girder, it is preferred to space the upper boom rod 1' off-center between the lower boom rods 1', l, as shown at 20 in FIG. 5a, so that the braces may be bent through an angle of about a line parallel to, and spaced from, upper boom rod 1.

In the modification of FIG. 6, the stubs 4 of the braces 2 have been bent over to provide support for a reinforcing grid or mat 5 mounted in a plane parallel to, and below, the lower boom of the lattice girder. The transversely extending rods 6 of the reinforcing mat or grid are simply moved into the space between the bentover portions of stubs 4, which extend longitudinally, and the lower boom rods 1', 1' to support the reinforcement on the girder.

The spot welding method for making the mat or grid, which serves as the blank for the production of the lattice girders, is schematically illustrated in FIG. 7. The spot welding machine 7 may be fixedly mounted or it may be rotatable about a vertical axis 8. If rotatable, the longitudinally extending structural steel rods 1, 1' are fed to the machine in the direction of their extension, and the machine is then turned about axis 8 to a desired angle determining the oblique extension of the transverse rods 2 in respect of the longitudinal rods 1, i.e., the feeding direction of the transverse rods. If the machine is fixed, the feeding direction of the longitudinal rods 1 is chosen according to the desired angle, as shown by the oblique arrow in FIG. 7.

The girder of FIGS. 8 to 10 has an upper boom rod 1 and a single lower boom rod 1, the two booms being interconnected by diagonally extending braces 2 which again extend in a plane oblique and transverse to the perpendicular planes passing through the girder booms. Similarly to the embodiment of FIG. 6, the stubs 4 of the braces are bent over to receive and support the transverse rods 6 of a reinforcing mat or grid 5. The bend of the stubs 4 is preferably such that a wedgeshaped space is formed between the bent stubs and the lower boom 1' to hold the rods 6 securely. The spot welds between the braces and the booms are shown at 10.

As shown in broken lines in FIG. 8, the stubs 4 'may also be downwardly bent to provide a spacing element 11. If desired, these spacing elements may be protected against corrosion by a synthetic resin coating or sleeve.

We claim:

1. A lattice girder comprising an upper boom, diagonally etending braces connected to the upper boom and having respective legs extending therefrom, the braces forming triangles whose apices are at the upper boom and whose leg ends define the bases of the triangles, a lower boom connected only to the ends of the brace legs on one side of the girder, the lower boom compris- 2. The lattice girder of claim 1, wherein the braces are bent at their apices about an axis extending longitudinally adjacent the upper boom.

3. The lattice girder of claim 1, wherein the stubs are inclined upwardly in respect of the lower boom structural steel rod whereby the spaces are wedge-shaped.

4. The lattice girder of claim 1, wherein the stubs have downwardly bent end portions. 

1. A lattice girder comprising an upper boom, diagonally etending braces connected to the upper boom and having respective legs extending therefrom, the braces forming triangles whose apices are at the upper boom and whose leg ends define the bases of the triangles, a lower boom connected only to the ends of the brace legs on one side of the girder, the lower boom comprising a structural steel rod, the leg ends and lower boom defining a base plane of the girder, stubs extending from the brace leg ends below the base plane and extending at least partially in the direction of the girder, whereby the structural steel rod and the stubs therebelow define spaces therebetween, and a reinforcing mat comprising transversely extending structural steel rods supported on said stubs, the transversely extending structural steel rods being disposed in said spaces.
 2. The lattice girder of claim 1, wherein the braces are bent at their apices about an axis extending longitudinally adjacent the upper boom.
 3. The lattice girder of claim 1, wherein the stubs are inclinEd upwardly in respect of the lower boom structural steel rod whereby the spaces are wedge-shaped.
 4. The lattice girder of claim 1, wherein the stubs have downwardly bent end portions. 